Research Needs for Rational LRFD Criteria

There are at least a dozen factors causing or influencing impact. Current design specifications consider only a few of these. Location of truck wheel loads within the traffic lanes on a bridge as specified in AASHTO can be interpreted in different ways. Extreme out of lane positions should be considered as special, not usual, cases. In the past engineering judgment was often used to provide extra thickness of material at points where corrosion probably would occur, or where if it did occur the damage would be significant. Today engineers use devious means to rationalize a perceived need for thicker deck slabs. Design of bridge railings is currently controlled by the need to restrain heavy trucks traveling at high speeds. Such design criteria produce costly and less than pleasing appearances on railings for small, low speed, lightly loaded bridges.